Optical micro-projection system and projection method

ABSTRACT

An optical micro-projection system comprising the following components: at least one laser light source ( 200, 400, 402, 600 ); at least one movable mirror ( 102, 103, 203 ) for deviating light from said light source to allow generation of images on a projection surface ( 104, 301, 303, 306, 603 ); a self mixing module for measurement of the distance ( 604 ) between the projection source and a projection surface, said self mixing module comprising:—at least one photodiode ( 401, 601 ) for monitoring the light emission power of the laser light source;—an optical power variation counter for counting optical power variations ( 605 ); successive displacements of said mirror allowing the self mixing module providing successive projection distance measurements of a plurality of points of said projection surface. A projection method for optical micro-projection system and a distance measurement method are also provided.

FIELD OF THE INVENTION

The present invention relates to an optical micro-projection systemcomprising at least one laser light source and at least one movablemirror, preferably of MEMS type. It also relates to a projection methodand a projection distance measurement method.

BACKGROUND OF THE INVENTION

The biological effects of electromagnetic radiation to human beings canbe divided into two categories, ionizing and non-ionizing radiation. Thefirst, ionizing radiation, is related to cosmic and x-ray wavelengthsand to nuclear radiation. The second, non-ionizing radiation is relatedto ultraviolet, visible, infrared, microwave, and radio wavelengths.Image and video projection devices works within the visible spectrum ofthe light, therefore, non-ionizing hazard has to be investigated andavoided while running the device.

Biological effects of non-ionizing radiation are dependent on thespectral region of the radiation (wavelength) and the duration of theexposure to the radiation. Furthermore, the damage to the eyes and skinis dependent on whether there was a single exposure (acute) or dailyexposure (chronic) to the radiation.

The eye, are generally considered to be the organ of the body which ismost susceptible to damage by radiation. The parts of the eye that canbe affected by radiation are the cornea, lens, eye fluid, and retina.Different light radiation affects the individual eye parts. The damageto any of the parts occurs when the light is absorbed by the parts. Thedamage that takes place is dependent on the ranges of the exposurelevels and the time of exposure.

Visible wavelengths of radiated frequency range from 390 nm to 750 nm,those wavelengths are generally refracted by the cornea and absorbed bythe retina.

The Maximum Permissible Exposure (MPE) of the eye to visible radiationswithin 400-700 nm wavelengths is about 0.001 W/cm2 for an exposure timeof 10 seconds. Therefore a method to prevent damage is needed tomaintain an exposure lower than the authorized MPE.

In addition, the eye is also sensitive to other wavelength that caninduce severe damage, in the ultraviolet and infrared and therefore fordevice using such wavelength, a method for preventing damage is alsorequired.

In the past years, many different types of electronic devices usinglaser units in order to perform one or more technical functions havebeen developed. Micro-projections systems are among these devices. Withthe growing demand for laser diode for various applications such astelecom and laser pointer device, the eye safety issue for human becamean issue and was mainly handled by different methods. The simplestmethod was to use stickers placed at the tip of the laser pointer deviceand warning the user to avoid any direct eye illumination with thelaser. Another method was to develop a specific driving electronics inorder to avoid any peak current in the laser diode if electrical failureoccurs or to completely switch off the current in the laser diode abovea certain current level.

More advanced technique where described in past for eye laser safety,using CCD detector coupled with the laser source. The CCD detectordetects the motion of an object or a person in its vision field andsends a signal to stop the laser in the case of a movement.

Other technique use motion sensor, such as accelerometers or/andgyroscope, coupled with the projection system and sense motion of theprojector itself, and then send a signal to the laser source to eitherswitch off or lower the intensity. Other techniques also have beentested in the past using capacitive sensor where one electrode is placedin the measurement tool and the human body acts as a second electrode.The human presence is then sensed by the created voltage shift betweenthese two electrodes.

A problem of these laser safety techniques, for the specific laserprojection application, is that none of these existing techniques arecompletely efficient, as the existing solutions do not prevent eyedamage if the user switches on the projector while he looks directlytoward the light source and while not moving. This specific aspect andpossible risk damaging the eye, is possibly one of the key stoppers forthe use of such laser projector by a large number of people andespecially by children. Moreover, most of these techniques are complexand expensive.

Another problem of the existing techniques to prevent eye damage is thatthe use of a CCD detector or capacitive detection do not allow having adirectional sensing and is typically much larger that the field ofprojection of moving object. The result is that a moving object placedoutside the field of projection, and then fully safe in terms of eyesafety, will be sensed by the CCD detector and will either stop of lowerthe projection intensity of the laser. For hand-held application oflaser projector, this working behaviour, even though allowing eye safetyapparatus is therefore not adapted to normal operation and use. Indeedthe user should be able to use the laser projector in a crowed place andshould be able to project while maintaining the projector in its hand,and during any motion.

A further problem of the eye safety technique while using laser source,is that the use of a CCD detector or an external motion sensor furtherincrease the complexity of the overall laser-based projection system byadding a different technology to the technology initially used for theprojection purpose.

A known type micro-projection systems based on Micro-Electro-MechanicalSystem (MEMS) is presented in FIG. 1A, where two MEMS scanning mirrors102 and 103 are reflecting a laser light source 101 is order to projecta two dimensional image on a target screen 104. Other projection system,presented in FIG. 1B and based on matrix of a large number of individualaddressable pixels 105, either based on either MEMS technology or LiquidCrystal on Silicon could also use laser source to project image.

A complete architecture for laser-based colour projection using twoOne-Degree-Of-Freedom (1 DOF) MEMS scanning mirrors is presented in FIG.2. The laser beams 200 are combined using a beam combiner 201 opticdevice and the resulting beam is entering a beam splitter 202 and isdeflected by the two MEMS scanning mirror 203 to project a twodimensional image. However, in existing projection systems, there is nocomplete safety system that can avoid eye damage when the eye is withinthe field of projection above the MPE limit, as presented in FIG. 3.

Other electronic devices using self-mixing technique are also known. Forinstance, WO2005/106634 discloses an apparatus for handling sheetmaterial or an optical input device, which employs a relative movementsensor utilizing the so-called “self-mixing” effect of a laser diode. Aband pass filter is provided for filtering the electric signal resultingfrom measurement of the electric signal to reduce or substantiallyeliminate the effects of both the low frequency carrier signal and thehigh frequency noise present in such a signal. As a result, theprecision of the laser self-mixing translation measurements issignificantly improved.

U.S. Pat. No. 6,233,045 relates to a self-mixing sensor usable forremotely measuring speed, vibrations, range, and length provided in amanner making the device practical for economic implementation whileretaining accuracy. In one embodiment, the device is configured to avoidmode hopping, such as by providing for relatively high loss for allmodes other than the desired mode. Preferably this is accomplished byutilizing laser types that have a high degree of side mode suppression,such as DFB lasers or through active or passive control of the amount oflight permitted to re-enter the laser.

However, these devices are of no use to provide micro-projection systemor methods.

WO2007/062154 relates to a method for compensating non-uniformities of aprojection surface in a front projection display. The measuredproperties of the surface are used to provide a screen compensationbitmap or a screen compensation convolution table. To obtain the screencompensation map, the method involves measurement of brightness for eachpixel and storing the related values in the map. The compensated imageis obtained in modifying the grayscale values of the pixels in the videoimage according to corresponding values in the screen compensation mapto produce a compensated video image signal.

According to this method, the applied correction directly depends on theprojected image. Thus, if an image showing an irregular surface such asa cushion or non ironed clothes or sheets, etc, is displayed, theprojection system will use the method to compensate the image as if theirregularities where caused by the projection surface. Moreover, thecorrection depends on the image taken by an additional camera or devicewhich is not perfectly aligned with the projection system, which adds tothe cost and complexity, and creates parallax errors. This device is ofno use for eye-safety.

US2009/0147272 describes a proximity detection method for controlling ofan imaging device. A proximity detector is capable of estimating thedistance from an object to the projector. If an object is detectedwithin a minimum distance, the projector operation may be altered, forexample to cause the projector to turn off or to reduce the intensity ofthe emitted light below a selected range. In a first embodiment, thedetection module uses periphery detection to detect the presence of anobject in front of the projector. The proximity detector projects nearlycollimated beams of infrared light to create spots that are placedaround a display region projected by a projector. The reflected beamsare then detected by a linear array of sensors, which detects reflectionof the beams within a detection cone. In a second embodiment, adetection module uses triangulation based distance estimation to detectthe presence of an object in front of the projector. Such a systeminvolves specific infrared emitters and detectors in addition to thestandard projection material. Distance data involve only few points,therefore limiting accuracy and potential other uses of the data. Again,the distance measuring system is not aligned with the projection system,creating parallax errors.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodand a device providing protection for human and animal bodies, and moreparticularly eye protection for humans during use of a laser projectionsystem.

It is another object of the invention to provide protection means for alaser projection system that do not interfere with the surroundingenvironment or do not provide false detection due to objects that arenot directly exposed to laser light.

It is a further objet of the invention to provide a protection for laserprojection system that is simple, reliable and cost effective.

It is a further object of the invention to provide a distancemeasurement method that is compatible for use with a micro projectionsystem.

According to the invention, these aims are achieved by means of anoptical micro-projection system comprising the following components:

-   -   at least one light source;    -   at least one movable mirror for deviating light from said light        source to allow generation of images on a projection surface;    -   at least one photodiode for receiving light reflected by said        projection surface;    -   a distance evaluation circuit for evaluating the distance        between the projection source and a projection surface based on        light deviated by said mirror and received by said photodiode.

Sharing a common deviation arrangement for illumination and distancemeasurement is particularly advantageous. For instance, distancemeasurement for each point or pixel is precisely based on the same pathfollowed by the lighting step, thus avoiding any parallax imprecision.

The distance evaluation system uses similar technology blocks, includinga light source, as the ones used for the projection system and thereforedoes not increase the complexity of the whole system by adding a newdifferent technology.

Distance measurement may be based on different technologies such astime-of-flight evaluation or self-mixing for instance.

The light source is advantageously a laser light source. In a variant,Digital Light Processing (DLP) technologies may be used with such asystem.

In a preferred embodiment, the distance evaluation circuit is arrangedfor evaluating the brightness of light deviated by the mirror andreceived by the photodiode in order to evaluate the distance.

In an aspect of the invention, the circuit comprises a self-mixingmodule and an optical power variation counter for counting optical powervariations (swings).

In another aspect of the invention, the same component is used as saidlight source and as said photodiode.

In a further aspect of the invention, the photodiode is an avalanchephotodiode, said distance evaluation circuit being arranged forevaluating the time-of-flight of the light between emission by saidlight source and detection by said avalanche photodiode.

In a further embodiment, the light source emits a modulated light at avisible wavelength, said mirror deviating said visible light so as toscan a visible image onto said projection surface, said photodiodereceiving said visible light reflected by said projection surface.

In a still further embodiment, the system further comprises at least onelight source emitting a modulated light at a visible wavelength, atleast one additional light source emitting infrared light at an infraredwavelength, and said mirror deviating said visible light and saidinfrared light, so as to scan a visible image onto said projectionsurface, said photodiode receiving said infrared light reflected by saidprojection surface.

In a preferred variant, successive displacements of said mirror allowdistance measurements of a plurality of points of said projectionsurface. Compiling the plurality of measured distances then allowsgenerating a projection distance map of the generated points.

The resulting distance map is particularly useful on the one end forenhanced safety, allowing detecting an object at any position, and onthe other end to enable further technical features, such as brightnesscorrection, image distortion detection, volume calculation, profiledetection, as further discussed here after.

In still another variant, the laser light source is an image projectionlight source usable alternatively in an image projection mode and in ameasuring mode during which the projection point does not correspond toan image pixel.

The mirror is preferably a MEMS scanning micro-mirror.

In another aspect, the self-mixing module further comprises a lightamplitude measurement unit for measurement of reflective light amplitudelevel on said projection surface. This enables the system to compensatefor brightness non-uniformity, by projecting brighter image portions inspecific zones and darker image portions in other zones.

The optical micro-projection system is advantageously based on DigitalLight Processing (DLP) of Liquid Crystal Display (LCD) or Liquid Crystalon Silicon (LCoS) matrix. The light source can also be a Light EmittingDiode (LED) or Super luminescent Light Emitting Diode (SLED).

In another aspect, the invention also provides a projection method foroptical micro-projection system comprising the steps of:

-   -   a) providing at least one light source coupled to at least one        movable micro-mirror for deviating light from said light source        to allow generation of images on a projection surface;    -   b) receiving light reflected by said projection surface with at        least one photodiode;    -   c) with a distance evaluation circuit, evaluating the distance        between the projection source and a projection surface based on        the output of said photodiode based on light deviated by said        micro-mirror and received by said photodiode.

In a preferred embodiment, successive displacements of said mirror allowdistance measurements of a plurality of points of said projectionsurface.

In a further embodiment, the method also comprise the following steps:

-   -   a) for a first point (for instance an image pixel) in a        projection zone, generating a laser light signal for projection        on a projection surface via reflexion on said micro-mirror;    -   b) measuring the projection distance of this point from the        projection source;    -   c) displacing the micro mirror position to a new position        allowing projecting a further point;    -   d) projecting said further point with said laser light source;    -   e) measuring the projection distance of this further point from        the projection system;    -   f) repeating steps “c” to “e” until the projection distances for        all points have been measured, and;    -   g) compiling the plurality of measured distances for generating        a projection distance map of the generated points.

Self-mixing technique is preferably used for distance measurement. Thistechnique is advantageously completed by optical power variationscounted with an optical power variation counter. Other ways of measuringthe distance are also possible, such as time-of-flight evaluation forinstance.

The light source arrangement differs in accordance with severalvariants. In a first variant, the light source is also used for imageprojection. In a second variant, the light source is used alternativelyin an image projection mode and in a measuring mode during which theprojection point does not correspond to an image pixel. In a thirdvariant, the light source is an infra-red laser diode used specificallyfor distance measurement.

In a preferred embodiment, the output power from the laser source isreduced if the measured distances indicate that for at least one point,the distance value is below a given threshold value.

Such a method enables for instance the detection of an object placed infront of the micro projector emission light cone and the subsequentreduction of the emitted light power in order to enable safety operationmodes. This is of particular interest, for instance in uses related toprevention, such as eye protection and other human and animal body partssafety apparatus. In such cases, the reduced power is preferably set tovalues such that the Maximum Permissible Exposure (MPE) of the eye isnot reached.

The projection method for optical micro-projection system may comprisethe step of determining the position of an object placed in theprojection cone.

The projection method may comprise the step of determining the profileof said object, and wherein the brightness of the image projected ontosaid object is reduced.

The projection method, wherein signals representative of the position ofsaid object are used as data commands for a graphical user interface.

The projection method for an optical micro-projection system, whereinsaid image is projected onto a semi-transparent projection surface, andwherein the position of an object behind said projection surface isdetermined.

The projection method for optical micro-projection system, wherein theposition of several objects simultaneously present in said projectioncone is determined.

The projection distance map may also be used for different purposes, ina plurality of applications, in particular, but not exclusively, formicro projection systems.

In a first variant, the projection distance map enables defining theprofile of an object or person placed in front of the expectedprojection surface. After such detection, the map can be used to projectaround said profile.

In a second variant, the projection distance map is used in order todetermine volume dimensions. Considering the high-resolution mapobtainable with this method, volumes may be measured in a very accurate,simple and reliable way. For applications such as quality control, wherelarge quantities of components have to be measured accurately andquickly, the present method is of particular interest. Volumemeasurements may also be precisely performed with components or objectshaving complex shapes or profiles.

In a third variant, the projection distance map is used in order todetect any image distortion. In case of such detection, a modulation ofthe mirror-scanning angle is calculated in order to compensate the imagedistortion.

In still a further variant, the projection distance map is used in orderto adjust the image size and power brightness. This may be done in orderto optimize the projection functionality, depending on user preference.

In a further aspect, the invention also provides a distance measurementmethod, in particular for an optical micro-projection system, comprisingthe steps of:

-   -   a) providing at least one laser light source coupled to a        movable micro-mirror and to a scanning control module for        deviating light from said light source for projection on a        projection surface;    -   b) receiving light reflected by said projection surface with at        least one photodiode;    -   c) with a measuring circuit using the same scanning control        module, evaluating the distance between the projection source        and a projection surface based on the output of said photodiode.

In a preferred embodiment, successive displacements of said mirror allowdistance measurements of a plurality of points of said projectionsurface and compiling the plurality of measured distances allowgenerating a projection distance map of the generated points.

In such a distance measurement method, the projection distance map isadvantageously used in order to either determine volume dimensions, ordetect any image distortion or to adjust the image size and powerbrightness.

Self-mixing technique or time-of-flight distance measurement techniquemay be used for distance measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other purposes, features, aspects and advantages ofthe invention will become apparent from the following detaileddescription of embodiments, given by way of illustration and notlimitation with reference to the accompanying drawings, in which:

FIGS. 1A and 1B describe known type laser projection systems basedrespectively on MEMS scanning micro-mirror and matrix of digitalmicro-mirror or Liquid Crystal on Silicon;

FIG. 2 describes a color projection system based on MEMS scanningmicro-mirror and multiple laser sources;

FIG. 3 describes an object in the field of projection of a projector;

FIG. 4 describes the electrical equivalent circuit of a laser diode;

FIG. 5A illustrates the working principle of the distance measurementtechnique;

FIG. 5B is a schematic representation of the main components of amicro-projection system according to the invention;

FIG. 5C is a schematic representation of the main components of avariant of a micro-projection system according to the invention;

FIG. 6 describes the system architecture for a projector using MEMSscanning micro-mirror and laser light source;

FIG. 7 describes the system block diagram for the laser projector;

FIG. 8 describes image distortion due to the projection on a non-flatsurface;

FIG. 9 describes the block diagram for the image distortioncompensation;

FIG. 10 describes the projection on a surface having various depths;

FIG. 11 describes a projection method allowing projecting images arounda human body.

FIG. 12 describes a projection system that interacts with the movementof the human body such as finger or hand.

DETAILED DESCRIPTION OF THE INVENTION

For clarity, as is generally the case in representation of microsystems,the various figures are not drawn to scale.

Laser diodes are made of two discrete components, a laser diode “LD” 400and a photodiode “PD” 401, as presented in FIG. 4, the first componentis used to generate the laser light while the second is used to monitorthe light emission power of the laser diode. For many applications thelaser diode and the photodiode are feedback looped to maintain theoptical output power of the laser diode constant, independently of theworking temperature.

A laser diode remote sensing technique described by Thierry Bosch in “Anoverview of self-mixing sensing applications” can be used to measuredisplacement, vibration, velocity and distance by using the OpticalFeedback Interferometry (OFI) properties inside the active cavity of thelaser diode 600 (see FIG. 5).

FIG. 5A presents the Self-Mixing “SM” technique that consists ininjecting a triangular waveform modulated current 602 into the laserdiode 600 to perform absolute distance 604 measurements of a stationarytarget 603. Indeed, by modulating the injected current, the length ofthe equivalent laser diode cavity is modified while the complexrefractive index of the active cavity is varying. Moreover, both theoptical frequency and power are also modulated. The emitted wavelength Xthen presents a triangular shift AX, therefore the wave number (2π/λ) isshifted by the amount (−2πΔλ/λ2). Optical power swings occur whileinjecting the current with a triangular waveform modulation. Theabsolute distance 604 measurement of a stationary target can beperformed by counting the N number of optical power swings 605 duringeach modulation cycle, detected with the integrated photodiode 601.

In alternative embodiments, absolute distance measurement may beperformed by evaluation of time of flight, based for example onavalanche photodiode triggered by single photons and Time to DigitalConverter “TDC”.

Micro-projection systems based on laser diode technology classically useone or two micro mirrors to deflect the light beam and generate theimage pixel by pixel. The invention uses the “SM” distance measuringtechnique coupled with one or two steering mirrors to determine thedistance of an object 302 placed in front of the micro-projector lightemission cone 300 as shown in FIG. 3. The laser diode used to performthe “SM” distance measurement can be the same one used as light sourcein the projection system. If needed, an additional laser diode can beadded to the projection system, in order to perform the distancemeasurement without disturbing the projection laser diodes.

FIGS. 5B and 5C show schematic representation of the main componentsinvolved in the micro-projection system of the invention. As shown inFIG. 5B, a laser diode 600 projects a laser light on a projectionsurface 603 via a scanning mirror 613. At least a portion of the lightis reflected on the projection surface and returns to a photodiode 601,adapted for monitoring the reflected light. A circuit is provided forevaluation of the distance between the projection system and theprojection surface. In the illustrated example, this circuit comprises aself-mixing module 610 and an optical power variation counter 611,cooperating with the laser diode 600 and the photodiode 601 and allowingdistance measurement using self-mixing technique. The self-mixing module610 and the optical power variation counter 611, using the multipledistances resulting from the measurement steps, provide projectiondistance maps 612, that may be used in further steps for differentapplications as explained hereafter.

FIG. 5C shows a variant in which at least one Infra-Red IR laser 614 isused. FIG. 6 shows an example of such variant where an additionalInfra-Red “IR” laser diode 402 is provided in order to perform thedistance measurement. As shown in FIG. 5C, a plurality of laser diodes600 is advantageously used, coupled or not to one or more IR diodes 614.

The advantage of using an additional IR laser diode, instead of one usedas projector light source, is the non disturbance of the projected imagewhile the system perform a distance measurement.

The device and method according to the invention enable performing adistance measurement over the entire projection surface 301. Thedistance measurement can be performed pixel by pixel while the system isrunning. As a result of the “SM” distance measurements, an objectdistance map (or projection distance map) with the same resolution (orwith a lower resolution) as the projected image can be generated andused for a plurality of applications. In a first example of application,the projection distance map is used to detect an eventual object placedin front of the micro-projector light emission cone 300. If the detectedobject is placed too close to the projector emission window 300 thelight intensity is automatically reduced, in order to stay under the MPEregion, no matter which kind of object is detected.

The method and device of the invention allows completely avoiding thehuman eye hazard by keeping the projected light intensity lower than theeye damage soil at visible wavelengths. An advantage of the inventionconsists on the fact that the laser projection system is always safe forthe human eye by instantly reducing the output power.

Another aspect of the invention is the innovative way of integrating the“SM” technique into the scanning laser based projection system. Indeedthe method and device according to the invention allow minimizing thesystem complexity and avoid any alignment issues, and insure that themeasurement system does not disturb the projection and degrade the imagequality.

As shown in FIG. 2, the device of the invention uses one of the laserdiode 200 already used as light source for the projection device inrelation with the SM technique in the following specific way: during thedistance measurement time-frame, no pixel of the image is projected withthe laser diode used for the distance measurement. In other words, ifone laser diode “lambda” is used to perform the distance measurement,during this time frame, either all other laser diodes are switched OFF,or they are pulsed as usually to project the image pixel, whereas theinitial laser diode “lambda” is actuated differently to perform thedistance measurement. For a three laser (RGB) projection for example,having the green and blue color still pulsing image pixel as usual couldlimit the image degradation. In fact, the normal pixel projection way isto pulse the laser using a short pulse. However, in order to use the SMtechnique, it is required to apply a triangular waveform to the laser.It is therefore not possible to do the measurement distance and theimage projection at the same time without degrading the projected imagequality. The required time-frame for doing the distance measurement, andtherefore the number of image pixel that will not be projected, dependson the normally used pixel pulsation speed.

Similar assembly technique can be used to assemble the IR laser sourceto the other optical components using passive alignment technique. Thistechnique has the further advantage to perform the distance measurementat the same time as the other lasers are used to project the image,while not disturbing the image projection quality. Furthermore, the IRlaser diode can be of lower power compared to the ones used as lightsources for the projection system. The lower power can be explained bythe higher sensitivity of photodiodes at IR wavelength. The IR laserdiode power is always lower than the MPE value for his correspondingwavelength, avoiding any possible eye injuries.

This fact then ensures eye safety from the IR source, always stayingunder the MPE region and a lower power consumption of the overallprojection-distance projection system.

In addition, such optical architecture enables to detect an object onlywithin the cone of projection 300 of the device, meaning only in therange that can be dangerous for the eye. The invention providesdirectionality of the distance measurement only in the needed scoperange because the IR light follows exactly the optical path of thevisible light. It then prevents to inadvertently reduce the powerintensity if an object is placed outside the projection cone, in a zonethat should not be taken into account. The complete expectedfunctionalities of the device are thus maintained.

FIG. 7 illustrates a further aspect of the invention. The block diagramexplains the relation between the distance measurement and the regulatedoutput laser power in order to stay under the MPE region with objects atany distances from the projector light source. In order to avoid anydamage during the starting up of the colour projection, in the case aperson put the projector in direct contact with the eye for example, afirst distance measurement is done with the low power IR laser, underthe MPE region. Then if the projection distance is sufficient tomaintain lower MPE limit, the visible laser sources are started. As themeasurement distance can be done at the same speed or faster than theimage pixel pulsation speed, any object of human entering the projectioncone can be detected fast enough to stay below the MPE exposure limit.The system is also designed to shut down all laser sources in case offailure of the distance measurement system and/or a failure of one ortwo MEMS micro mirrors.

FIG. 8 illustrates another aspect of the invention related to the use ofsuch integrated measurement system in the projector in order tocompensate for the optical projection distortion that arises when theprojector projects non-perpendicularly to the projection surface 303.Indeed, using the SM measurement technique, not only the distance fromthe projector to the projection surface can be measured but also theeffective image size and shape on the projection surface. Thismeasurement also gives the information on the parallelism of the imageon the projected surface. Therefore, as the width of each scanning linecan be measured with the described measurement system, the projectionsystem is provided with a loop control in order to modulate the scanningangle or to alter the scanning pattern in order to compensate for theoptical distortion, as presented in the block diagram of FIG. 9. Theinitial distorted image 304 can then be restored 305 according to theproposed algorithm.

In a further aspect of the invention, the projection distance map isused to measure the distance of any object placed into the projectioncone. As the number of measurement points can be very high, a highresolution can be achieved. Because of the use of laser light source,measurement in harsh environment and especially outdoor and long-rangemeasurement can be achieved.

Still a further aspect of the invention relates to the optimization ofuse of such projection system. Indeed for the user point of view, one ofthe main concerns is to maximize the brightness of the projector,especially in bright environment, while staying below the MPE region. Todo this, the information provided by the measurement distance is used tocommand the scanning mirror angle and then the projection size is orderto maximize the projection brightness. Indeed, as presented in FIG. 10,in the case of a user projecting an image on a non-flat surface 306 thatcan even have various depth and cavities, the projector brightness isautomatically adapted to stay below the MPE region based on the shortestdistance between the projector and the projection support. However inthis specific case, the projector capabilities and brightnessfunctionality are greatly reduced due to the presence of a small area onwhich maybe the user would not want to project.

According to this further aspect of the invention, when the measureddistance between the projector and the projection support showvariations that can be linear or nearly-linear due to the projection ona curved surface, or that can be abrupt, as seen in FIG. 10, theprojector either proposes to the user or performs automaticallymodulation of projection scanning angle in order to evaluate the optimumprojection characteristics on a given surface. In the case presented inFIG. 10, the optimum could be to reduce the projection size to fit into309 opening and then being able to increase the output power from theprojector to achieve a brighter image, which was previously limited bythe presence of the 306 surface. This optimum could be differentdepending on the applications and can be either the brightness or theimage size.

In another aspect of the invention, the micro-projection system detectsthe presence of an object or a human body within the projection fieldand projects an image all around that object, as presented in FIG. 11.This technical feature enables interactivity, where a person 406 forexample can be placed in a “virtual” scene 405 that is projected aroundhim or her.

In a further application, the micro-projection system is adapted tomeasure the distance between the projector and an object at a highnumber of points, allowing calculating the volume of the object. Thesystem is then suited for three-dimensional measurement.

In a further application of the invention, the system is able to sensein two or even three dimensions the position of a fix or moving object,as shown in FIG. 12, that could be for example a human hand, finger or astick or even the spot light coming from a laser pointer. Thisinformation on position can be retrieved by the processing system thatcommands the micro-projection system, and used as an additional inputchannel, for example in order to adapt the projected image according tothe position of this object. The motion of such object could also besensed and the projected image can be changed accordingly. With thissystem, it is possible to do close to real time evaluation of positionand speed of an object, but it is also possible to sense the positionand speed of multiple objects simultaneously, for example in order toprovide signals representative of the 2D or 3D position of objectswithin the projection cone, and to command the processing systemaccordingly.

A typical application of such a system is a human-machine interface toprovide interactivity. The projected image 407 could have some specificparts, 408 or 409 for example, that can be dedicated for the objectsensing and motion and where the image brightness remains below the MPEregion or lower, such as class 1 or class 2, in order to prevent anyinjury of a person moving in this portion of the image. The rest of theprojected image may be brighter. The projected image may also comprisewidgets, such as buttons, scrolling elements, sizable windows, etc whichcan be manipulated by a user for entering commands. Other body and handgestures may be executed in front of (or behind) the projection surfacein order to enter command. For example, a displacement of the arm, or ofthe fingers, may be used for scrolling, panning, or for moving an objectin 3 dimensions. Moving arms apart or together can be used for resizingobjects.

The projected image may also be adapted to the position, size and motionof the object, in order to project onto this object, and/or around thisobject.

In one embodiment, the image is projected onto a semi-transparent screen411; in this case, an object behind the projection surface, such as ahuman body 410, could also be sensed.

In any cases, it is not mandatory that the object whose position issensed is in contact with the projected image screen: an object can alsobe sensed if it is placed away from the screen.

The system and method of the invention may use either laser visible orinfrared source, but all light sources having integrated photodiode canbe used, such as Superluminescent Light-Emitting Diodes (SLED) orLight-Emitting Diode (LED) light sources.

Another aspect of the invention is that the system is adapted to have afeedback on both the distance measurement from the projector to thesupport and the amplitude of the reflected light. This enables thesystem to determine information about the projection support brightness.Indeed due to the light absorption that depends on the support colour orroughness, the system is able to control the laser power intensity inorder to adapt it for the support brightness. As an example, whenprojecting onto a surface that have bright, grey and dark zones, theprojector is able to compensate for the different zones and then give tothe user a better visual comfort with uniform or adapted projectionbrightness.

Those skilled in the art will also understand that the here abovedescribed materials can be modified. Such alterations, modifications andimprovements are intended to be within the spirit and scope of theinvention. For instance, the projection system may be a matrix-basedprojection system such as LCOS, DLP and LCD.

Accordingly, the foregoing description is by way of example only and isnot intended to be limiting.

1-15. (canceled)
 16. A system comprising: a light source; a MEMS mirrorin optical communication with the light source, the MEMS mirror todeviate light from the light source to illuminate a projection surface;a photodiode to receive light reflected by the projection surface; adistance evaluator to: determine a distance between the light source andthe projection surface; and detect a change in the determined distance;and a light source adjuster to adjust the light source and the MEMSminor based in part on the determined distance and the detected changein the determined distance to modify a property of a projected image onthe projection surface.
 17. The system of claim 16, the detected changein the determined distance based at least in part on a physicalinteraction of a user with a part of the system or the projectionsurface.
 18. The system of claim 16, the distance evaluator to detectthe change in the determined distance based on light deviated by theMEMS mirror and received by the photodiode.
 19. The system of claim 16,the light source comprising a laser.
 20. The system of claim 16, thedistance evaluator to receive a first signal from the light source, thefirst signal to include an indication of an intensity of light emittedby the light source and receive a second signal from the photodiode, thesecond signal to include an indication of an intensity of light receivedby photodiode, the distance evaluator to determine the distance based onthe first signal and the second signal.
 21. The system of claim 16, thelight source comprising the photodiode.
 22. The system of claim 16, thelight source emitting a modulated light at a visible wavelength, theMEMS minor deviating the visible light to scan a visible image onto theprojection surface, the photodiode to receive the visible lightreflected by the projection surface.
 23. The system of claim 16, thelight source comprising: a first light source to emit a modulated lightat a visible wavelength; and a second light source emit infrared lightat an infrared wavelength, the MEMS mirror to deviate the visible lightand the infrared light onto the projection surface, the photodiode toreceive the infrared light reflected by the projection surface.
 24. Thesystem of claim 16, the distance evaluator to: determine a distancebetween the light source and a plurality of points on the projectionsurface; and generate a projection distance map of the projectionsurface based on the plurality of determined distances.
 25. The systemof claim 16, the light source to emit a first light pattern to projectan image onto the projection surface and to emit a second light patternto project light onto the projection surface to measure a distancebetween the light source and the projection surface.
 26. A methodcomprising: receiving, at a MEMS minor, light emitted from a lightsource; deviating the received light onto a projection surface;receiving light deviated by the MEMS minor and receiving the reflectedby the projection surface; determining a distance between the lightsource and the projection surface based at least in part on the receiveddeviated light the received reflected light; detecting a change in thedistance between the light source and the projection surface; andadjusting at least one of the light source or the MEMS minor to adjust aparameter of an image projected onto the projection surface by the lightsource.
 27. The method of claim 26, the detected change in thedetermined distance based at least in part on a physical interaction ofa user with a part of the system or the projection surface.
 28. Themethod of claim 26, comprising detecting the change in the determineddistance based on the received deviated light and the received reflectedlight.
 29. The method of claim 26, the light source comprising a laser.30. The method of claim 26, comprising: receiving a first signal fromthe light source, the first signal to include an indication of anintensity of light emitted by the light source; receiving a secondsignal from a photodiode, the second signal to include an indication ofan intensity of light received by photodiode; and determining thedistance between the light source and the projection surface based onthe first signal and the second signal.
 31. The method of claim 26,comprising: receiving modulated light at a visible wavelength; receivinginfrared light at an infrared wavelength; deviating the visible lightonto the projection surface to project an image onto the projectionsurface; and deviating the infrared light onto the projection surface todetermine the distance between the light source and the projectionsurface.
 32. The method of claim 26, comprising: determining thedistance between the light source and a plurality of points on theprojection surface; and generating a projection distance map of theprojection surface based on the plurality of determined distances. 33.The method of claim 26, comprising: emitting a first light pattern toproject an image onto the projection surface; emitting a second lightpattern to project light onto the projection surface to measure adistance between the light source and the projection surface.
 34. Anapparatus comprising: a MEMS mirror in optical communication with alight source, the MEMS mirror to deviate light from the light source toilluminate a projection surface; a photodiode to receive light reflectedby the projection surface; logic, at least a portion of which is inhardware, the logic to: determine a distance between the light sourceand the projection surface; and detect a change in the determineddistance; and a light source adjuster to adjust the light source and theMEMS minor based in part on the determined distance and the detectedchange in the determined distance to modify a property of a projectedimage on the projection surface.
 35. The apparatus of claim 34, thedetected change in the determined distance based at least in part on aphysical interaction of a user with a part of the system or theprojection surface.
 36. The apparatus of claim 34, the logic to detectthe change in the determined distance based on light deviated by theMEMS minor and received by the photodiode.
 37. The apparatus of claim34, the logic to: determine a distance between the light source and aplurality of points on the projection surface; and generate a projectiondistance map of the projection surface based on the plurality ofdetermined distances.